PROJECT SUMMARY/ABSTRACT The ability to switch between metabolic substrates based on their availability, metabolic flexibility, requires a complex network of molecular interactions for efficient function. We have found that one aspect of this network is the control of mRNA transcript levels by HuR. HuR is an RNA-binding protein that regulates levels of RNA transcripts and their translation within cells. Though HuR has been extensively studied for its roles in proliferation, inflammation, and apoptosis, its action as a metabolic sensor is relatively unknown. Our preliminary data indicate that skeletal muscle specific HuR knockout mice show increased insulin resistance and adiposity relative to control animals. Interestingly, these mice show increased levels of HuR target transcripts, while also showing decreased translated protein levels for these transcripts. The poor metabolic prognosis resulting from down regulation of HuR in skeletal muscle also complements data we have collected for metabolically unhealthy male and female human skeletal muscle samples. The proposed aims will therefore test the hypothesis that delivery of HuR target transcripts to the ribosome promotes metabolic flexibility by influencing the mTOR signaling pathway. Very important is the new methodological techniques that Dr. Warfel will learn in order to develop his career as an independent investigator focused on RNA biology and metabolism. Methods in this proposal include transgenic mouse model generation and phenotyping, use of metabolic chambers and radioactive metabolite assays, bioinformatics and molecular biology. The training in these techniques will also provide the preliminary data necessary to develop future projects aimed at understanding the contribution of RNA binding proteins to cellular metabolic homeostasis, and to consider new potential avenues in the treatment of insulin resistance and obesity. This is Dr. Warfel?s long-term research expectation, and he has assembled an outstanding team of mentors and collaborators with extensive experience in areas relevant to this proposal who will provide guidance to ensure that Dr. Warfel achieves independence.